JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        Let\[f\]be a twice differentiable function such that\[f(x)=-f(x)\]and\[f(x)=g(x)\]. If\[h(x)=[f{{(x)}^{2}}+g{{(x)}^{2}}]h(1)=8\]and\[h(0)=2,\]then\[h(2)\]is equal to

    A)  1                                            

    B)  2

    C)  3                                            

    D)  None of these

    Correct Answer: D

    Solution :

                    \[h(x)=[f{{(x)}^{2}}+g{{(x)}^{2}}]\] \[\Rightarrow \] \[h\,(x)=2f(x)f(x)+2g(x)g(x)\] \[\Rightarrow \] \[h\,(x)=2f(x)g(x)+2g(x)f\,(x)\]                                                 \[\left[ \begin{align}   & \because g(x)=f\,(x) \\  & \Rightarrow g(x)=f\,(x) \\ \end{align} \right]\] \[\therefore \] \[h\,(x)=2f(x)g(x)+2g(x)(-f(x))\]                                                 \[[\because f\,(x)=-f(x)]\] \[\Rightarrow \]\[h\,(x)=0\] \[\Rightarrow \] \[h(x)=C,a\] a constant for all \[x\in R\] \[\Rightarrow \] \[h(x)=Cx+{{C}_{1}}\] \[\Rightarrow \] \[h(0)={{C}_{1}}\]and   \[h(1)=C+{{C}_{1}}\] \[\Rightarrow \]               \[2={{C}_{1}}\]and          \[8=C+{{C}_{1}}\] \[\Rightarrow \]               \[{{C}_{1}}=2\]and          \[C=6\] \[\therefore \]  \[h(x)=6x+2\] \[\Rightarrow \]               \[h(2)=6\times 2+2=14\]


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